Heater for tube reactors

ABSTRACT

In a tubular reactor carrying a bed of solid material into which carbon electrodes project for heating the material upon passage of a current, the outside ends of said electrodes being connected to metallic conductors in turn connected to a supply of current, the invention involves pouring lead about the end of each electrode to effect improved contact between the electrode and its respective metallic conductor. The process involving use of such electrodes to react carbon with chlorine and the oxide of silicon or metals such as vanadium, titanium or zirconium is also covered.

[451 Aug. 21, 1973 United States Patent 91 Langenhoff et al.

[ HEATER FOR TUBE REACTORS [75] Inventors: Ferdinand Langenhoff, Ranzel;

Erich Termin, Laufenburg; Otto Bleh, Bergheim, Sieg; Rico Kolb,

Ranzel, all of Germany [73] Assignee: Dynamit Nobel AG, Troisdorf,

Postfach, Germany Nov. 20, 1970 [22] Filed:

ABSTRACT 211 App]. No.: 91,408

In a tubular reactor carrying a bed of solid material into [30] Forelgn Apphcanon Prlomy Data which carbon electrodes project for heating the mate- Sept. 16, 1969 Germany................... P 19 46 718.6 rial upon passage ofa current, the outside ends of said electrodes being connected to metallic conductors in [52] U.S. 23/277 R, 13/23, 13/15,

turn connected to a supply of current, the invention involves pouring lead about the end of each electrode to effect improved contact between the electrode and its respective metallic conductor. The process involving use of such electrodes to react carbon with chlorine and the oxide of silicon or metals such as vanadium, titanium or zirconium is also covered.

[56] References Cited UNITED STATES PATENTS 2,681,943 6/1954 Hartwick....................... 23/277 R X 3 Claims, 1 Drawing Figure Patented Aug. 21, 1973 C/ gas ,INVENTORS BURGESS. DINKLAGE & SPRUNG ATTORNEYS HEATER FOR TUBE REACTORS The invention relates to electrically heated tubular reactors.

It is known to effect chemical reactions in tubular reactors wherein heating is effected electrically. For example, a quartz resistance coil has been positioned inside such a reactor and a current passed therethrough to heat up the coil and, thereby, the material within the reactor. After a time, however, the quartz becomes brittle. Moreover, the quartz is not sufficiently resistant to mechanical stresses. Finally,- while quartz may be useful in many applications it will not stand up in the case of long term use in the presence of carbon.

Attempts to use carbon electrodes to heat such reactors have not proven satisfactory, especially where chlorine is present, due to the difficulty of maintaining good contact between the carbon and a metal conductor. The carbon electrodes being porous and permeable to chlorine, it has not been possible heretofore to provide proper electric contact from carbon to metal. After a time, contact would be lost, probably through corrosive action of chlorine on the metal. Attempts to maintain contact by using chlorine-resistant metals such as nickel or silver as contact metal have been unsuccessful, as have attempts to render the electrodes impermeable to chlorine by impregnating with waxes, resins etc. lmpregnation with lead salt solutions, disclosed in Russian Patent No. 197,529, has also not been successful.

It is accordingly'an object of the present invention to provide an electric heating system for a tubular reactor which isefficient, long lived and simple.

It is a further object of the invention to provide a carbon electrode for an electric heating system for tubular reactors which is so connected as to be usable even in the presence of chlorine.

These and other objects and advantages of the invention are realized in accordance with the present invention which relates to an electric heating system for tubular reactors, used particularly for reacting metal oxides or silicates with chlorine in the presence of carbon, which system is characterized by carbon electrodes extending through gas-permeable electrically insulating inert layers and projecting into a bed of carbon surmounted by a porous insulating layer of inert material which forms a base onto which a solid reactant can be placed, the lower ends of the electrodes being encased by cast lead into a contact head.

Advantageously the electrode shaft is surrounded by a refractory chlorine-resistant electrically insulating tube extending down into the area cast about with lead. The tops of the electrodes may appropriately be rounded or beveled on one or both sides.

The invention will now be described more particularly with reference to the accompanying drawing which is a truncated vertical section through the tubular reactor.

Referring now more particularly to the drawing, carbon electrodes 1 are so arranged in the lower part of a reactor 2 as to provide a sufficient distance between the electrodes. The distance will depend on the reactor diameter and, in the preferred embodiment, is about 30 to 40 cm using a reactor which has an internal diameter of about 70 cm and a height of about 2.5 m, Le. a height:width ratio of almost 4. The diameter can be as small as 20 cm in which case the electrode spacing may be only cm or less, or with larger reactors the spacing may be 100 cm or more, all other dimensions being similarly scaled up.

Preferably the electrode head is not cylindrical but ratheris square, rounded, or beveled on one or both sides since then the spacing between electrodes can be varied by rotating the electrodes about their axes. As shown in the drawing, the ends of the electrodes 1 are angled and one is turned relative to the other.

The electrode portion below the head to above the electrode flange 3 is provided with a refractory chlorine-resistant electrically insulate-d tube 4 which may be of quartz, glass, quartz ware or the like. The bottom ends of the electrodes and of tubes 4 are embedded in lead in water-cooled contact heads 5. The lead seal 6, surprisingly enough, has proved the optimal solution. to the problem of electric carbon-to-metal contact under the action of chlorine.

The contact head is electrically insulated from the reactor floor by using an electrically insulating gasket and electrically insulating bushing washers 7.

A silvered copper bar 8 is welded to the contact head, establishing contact with the source of electric current. The reaction chamber generally has a refractory and electrically insulating liner 9. Electrical insulation is required in any event to avoid misrouting of the electric current. In a surface heatingsystem of fairly large diameter, a plurality of pairs of electrodes arranged crosswise may be used. The insulation from the reactor floor is provided by an asbestos packing 10 and for example fusible corundum fills 11 about 3 cm deep (grain size 3-5 mm). Fills of MgO, ZrO SiO or the like may also be used.

The space between electrodes is filled with carbon 12. Since disintegration of brittle fragments may give rise to cavities which might interrupt the flow of current, whereas round particles will roll together and function reliably, spheroidal graphite has been found best as the material making up the carbon bed. Besides, the balls provide excellent chlorine gas circulation and distribution as the gas required for the reaction passes through the bed. The bed of graphite spheres 12 is surmounted by another insulating layer 11 which forms a floor of the reaction chamber of the reactor. Onto this layer there is supplied intermittently or continuously, (by means not shown) a mixture of very fine grained solid reactants, e.g. vanadium pentoxide and carbon powders, which react with the gas passing. through the reactor. The bed of solid reactants 17 is relatively shallow, e.g. about 5 to 30 cm, which permits careful control of the temperature of the reaction, he the high temperatures are required over a relatively large area but only a short distance verticallyrl The reactor is also provided, as shown, with inlets 13 a vertical reactor, but with appropriate modification the gas could pass downwardly or the reactor could even be horizontal.

In the special case to which this invention is chiefly addressed, energy is supplied to a system subject to temperature fluctuations and steady loads from. about 200 to 1300C. In addition, the system is exposed to severe chemical stress, since these temperaturesare to be maintained in the presence of chlorine, carbon and reaction gases such as for exampleVOCh, TiCl,, ZrCl SiCl C0, C0,, COCl etc., that is to say, reducing and oxidizing agents at the same time. Specifically, the object is to carry out reductive chlorination reactions and to produce chlorides in accordance with the following equations, by way of example:

a. V 2 C 3 Cl .91 2 VOCl C0, CO

b. Tio 2 c 2 c1 TiCl, 2 co 0. Zrsio, 4 c 4 cl, ZrCl, sicl, 4 CO The heating system must be inside the reactor and sealed off gastightfrom the outside atmosphere without interfering with the flow of current. Besides, there must be complete electrical insulation from the metal shell of the reactor. The illustrated reactions are not true fluidized bed reactions but merely quasi-fluidized bed reactions since the gas flow velocities are not very high.

The invention will be further described in the following illustrative examples.

EXAMPLE I A chlorination process to produce VOCl according to equation (a) was carried out using a heating system according to the drawing in a reactor 600 mm in diameter and about 4 times as high. The electrodes were spaced apart about 35 cm and the inert layers 11 were magnesia particles, larger than 3 mm, and about 4 cm high. Powdered VOCl and carbon reactants were supplied intermittently to maintain a layer of about 5 to 30 cm thickness. The electrodes were supplied with alternating current at V and 160 A; after 3 hours, the temperature of the reaction chamber was 500C. The heating system was switched off and on again on several occasions and the process ran smoothly for half a year.

EXAMPLE II in a reactor 300 mm in diameter, a chlorination reaction according to equation (c) was carried out. The electrodes were energized with 10 V and 1000 A alternating current. After 4 hours, the temperature of the reaction chamber was l000C. After 4 weeks of operation, only insignificant manifestations of use were perceptible in the bed and on the electrodes.

It will be appreciated that the instant specification and examples are set forth by way of illustration and not limitation and that various modifications and changes may be made without departing from the spirit and scope of the present invention.

What is claimed is:

1. In a tubular re'actor having a base for supporting a material such as a bed of carbon, means for introducing a gas into said bed, an electric heating system for said bed including carbon electrodes projecting from outside said reactor into said bed, and means for connecting the ends of said electrode outside said reactor to metallic conductors in turn connected to a supply of electric current, the improvement comprising a gastight tube of refractory, electrically insulated material surrounding each electrode along its entire length from a location inside said reactor through said base toward the outside electrode end, means surrounding the out side end of said tube and defining therewith a chamber, said connecting means comprising a body of lead in said chamber about each electrode end and outside tube end and in contact with a respective metallic conductor to make improved contact therebetween, each body of lead extending to said tube so as to form therewith a gas-tight seal about the outside end of its electrode.

2. A reactor according to claim 1, wherein the end of each electrode extending into said bed is asymmetrical relative to the electrode axis, whereby upon rotation of an electrode about its axis the distance from said end to the corresponding end of another electrode may be varied.

3. A reactor according to claim 1, wherein said tube is made of refractory chlorine-resistant material.

It t i I i 

2. A reactor according to claim 1, wherein the end of each electrode extending into said bed is asymmetrical relative to the electrode axis, whereby upon rotation of an electrode about its axis the distance from said end to the corresponding end of another electrode may be varied.
 3. A reactor according to claim 1, wherein said tube is made of refractory chlorine-resistant material. 